On Simchas Torah we conclude the reading of the Torah in Deuteronomy and immediately begin another cycle with the first portion of Genesis. This symbolizes that the Torah, like a circle, is without end; its beginning and end are forever intertwined.
By reading the last portion and the first portion of the Torah contiguously, we connect the miraculous wonders performed by Moses to Creation. In other words, all the marvelous happenings in Egypt and the Wilderness were to impress upon the Israelites that there is a Creator Who rules the universe and conducts it as He wishes.
Without an ultimate goal, life is futile, and there can hardly be an ultimate goal in a universe that happened to come about through the accidental interaction of impersonal, mechanical forces. Furthermore, there can be no joy in a life that is futile, and indeed, people who feel that life is futile are apt to seek to escape from it rather than live it to its fullest.
The joy of the Succos festival reaches its zenith on Simchas Torah, and celebration of this joyous day is based on the awareness that our lives are purposeful and meaningful. The teachings and miracles of Moses, which instilled within us the faith that God created heaven and earth, are thus the key not only to the joy of the day, but to that of the entire year.